Various prior art devices are known which allow a user to insert a catheter/guidewire means into a body cavity or blood vessel allowing the user to deliver an inflatable balloon, cutting device or other therapeutic means to a desired area. In carrying out such procedures, which may be generally described as either angioplasty or atherectomy, the objective is to open a stenotic segment of a blood vessel.
Angioplasty uses an inflatable dilatation balloon positioned in the artery to dilate the arterial lumen at the stenosis. A typical angioplasty device is disclosed in Bhate et al., U.S. Pat. No. 4,896,669. The angioplasty device of Bhate et al. includes an inflatable balloon which is attached to the distal end of a hollow catheter. The proximal end of the catheter is attached to a fluid source, providing fluid communication between the balloon and the fluid source.
To treat an arterial stenosis, the Bhate et al. balloon is introduced into the artery in a deflated state and guided through the artery over a guidewire to a position adjacent to the stenosis. Fluid from the fluid source is then infused into the balloon via the catheter to inflate the balloon. As the balloon expands, it dilates the lumen of the artery. The balloon is then deflated and removed from the artery.
While effective for dilating the lumen at the stenosis, angioplasty devices, such as the Bhate et al. device, do not remove plaque from the artery. Consequently, residual plaque either remains in place at the point of the stenosis or breaks off and migrates to other locations in the blood stream. In either case, the plaque remains a continuing threat to create blockages in the circulatory system. To address the shortcomings of angioplasty, a procedure termed atherectomy has been developed, whereby plaque comprising the stenosis is cut and removed from the blood vessel.
An atherectomy procedure typically includes inserting a guidewire into an affected artery and advancing a cutting device having a hollow shaft over the guidewire until the cutting device is positioned adjacent to the stenosis. The cutting device is then advanced into the stenosis to cut a channel through the plaque, thereby increasing blood flow through the artery. The resulting plaque fragments can be removed from the blood stream, for example, through the shaft of the cutting device, or if the fragments are sufficiently small, they can be removed from the blood stream by the body's reticuloendothelial system.
A number of atherectomy devices are known in the art. Farr et al., U.S. Pat. No. 4,895,166, discloses an atherectomy device having a frustum-shaped cutter which is attached to the distal end of a hollow catheter. The cutter has two openings that define two straight, even cutting blades. The cutter is directed through the artery over a guidewire, and it is rotated as it advances into the stenosis, thereby cutting the plaque. Excised plaque enters the openings of the cutter and is subsequently removed through the hollow catheter.
Auth, U.S. Pat. No. 4,990,134, describes a rotational ablation system which is itself an improvement upon the invention described in Auth, U.S. Pat. No. 4,445,509. The '134 patent teaches the use of an ellipsoidal abrading head, or burr, coated with tiny diamond chips (shovels). The abrading head rotates and causes differential cutting, whereby the abrading head differentiates between inelastic plaque, which is removed, and elastic arterial tissue, which remains undamaged. More specifically, it is taught that a tip (burr) of the type described, operating at a tip velocity of at least about 40 ft./sec., is able to abrade inelastic material at a high removal rate, while generating microscopic particles (on the order of 5 microns or less) and leaving behind a tissue base having a smooth appearance on the surface of the wall of the vessel from which an abnormal deposit has been removed.
Currently available rotational ablation devices such as those described in U.S. Pat. Nos. 4,445,509 and 4,990,134 employ a single cutting or abrading burr which is permanently attached to the rotating shaft of the rotational ablation device. Often burrs of different sizes are required during a procedure, and thus it is necessary to use an entirely new rotational ablation device each time the cardiologist desires to employ a burr of a different size. It has, therefore, been recognized that it would be advantageous to provide for a rotational ablation device which allows one to utilize different cutting or abrading burrs of varying sizes and configurations.